v8-function-callback.h

// Copyright 2021 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef INCLUDE_V8_FUNCTION_CALLBACK_H_
#define INCLUDE_V8_FUNCTION_CALLBACK_H_

#include <cstdint>
#include <limits>

#include "v8-internal.h"      // NOLINT(build/include_directory)
#include "v8-local-handle.h"  // NOLINT(build/include_directory)
#include "v8-primitive.h"     // NOLINT(build/include_directory)
#include "v8config.h"         // NOLINT(build/include_directory)

namespace v8 {

template <typename T>
class BasicTracedReference;
template <typename T>
class Global;
class Object;
class Value;

namespace internal {
class FunctionCallbackArguments;
class PropertyCallbackArguments;
class Builtins;
}  // namespace internal

namespace debug {
class ConsoleCallArguments;
}  // namespace debug

namespace api_internal {
V8_EXPORT v8::Local<v8::Value> GetFunctionTemplateData(
    v8::Isolate* isolate, v8::Local<v8::Data> raw_target);
}  // namespace api_internal

template <typename T>
class ReturnValue {
 public:
  template <class S>
  V8_INLINE ReturnValue(const ReturnValue<S>& that) : value_(that.value_) {
    static_assert(std::is_base_of<T, S>::value, "type check");
  }
  // Handle-based setters.
  template <typename S>
  V8_INLINE void Set(const Global<S>& handle);
  template <typename S>
  V8_INLINE void SetNonEmpty(const Global<S>& handle);
  template <typename S>
  V8_INLINE void Set(const BasicTracedReference<S>& handle);
  template <typename S>
  V8_INLINE void SetNonEmpty(const BasicTracedReference<S>& handle);
  template <typename S>
  V8_INLINE void Set(const Local<S> handle);
  template <typename S>
  V8_INLINE void SetNonEmpty(const Local<S> handle);
  // Fast primitive number setters.
  V8_INLINE void Set(bool value);
  V8_INLINE void Set(double i);
  V8_INLINE void Set(int16_t i);
  V8_INLINE void Set(int32_t i);
  V8_INLINE void Set(int64_t i);
  V8_INLINE void Set(uint16_t i);
  V8_INLINE void Set(uint32_t i);
  V8_INLINE void Set(uint64_t i);
  // Fast JS primitive setters
  V8_INLINE void SetNull();
  V8_INLINE void SetUndefined();
  V8_INLINE void SetFalse();
  V8_INLINE void SetEmptyString();
  // Convenience getter for Isolate
  V8_INLINE Isolate* GetIsolate() const;

  // Pointer setter: Uncompilable to prevent inadvertent misuse.
  template <typename S>
  V8_INLINE void Set(S* whatever);

  // Getter. Creates a new Local<> so it comes with a certain performance
  // hit. If the ReturnValue was not yet set, this will return the undefined
  // value.
  V8_INLINE Local<Value> Get() const;

 private:
  template <class F>
  friend class ReturnValue;
  template <class F>
  friend class FunctionCallbackInfo;
  template <class F>
  friend class PropertyCallbackInfo;
  template <class F, class G, class H>
  friend class PersistentValueMapBase;
  V8_INLINE void SetInternal(internal::Address value);
  // Default value depends on <T>:
  //  - <void> -> true_value,
  //  - <v8::Boolean> -> true_value,
  //  - <v8::Integer> -> 0,
  //  - <v8::Value> -> undefined_value,
  //  - <v8::Array> -> undefined_value.
  V8_INLINE void SetDefaultValue();
  V8_INLINE explicit ReturnValue(internal::Address* slot);

  // See FunctionCallbackInfo.
  static constexpr int kIsolateValueIndex = -2;

  internal::Address* value_;
};

/**
 * The argument information given to function call callbacks.  This
 * class provides access to information about the context of the call,
 * including the receiver, the number and values of arguments, and
 * the holder of the function.
 */
template <typename T>
class FunctionCallbackInfo {
 public:
  /** The number of available arguments. */
  V8_INLINE int Length() const;
  /**
   * Accessor for the available arguments. Returns `undefined` if the index
   * is out of bounds.
   */
  V8_INLINE Local<Value> operator[](int i) const;
  /** Returns the receiver. This corresponds to the "this" value. */
  V8_INLINE Local<Object> This() const;
  /**
   * If the callback was created without a Signature, this is the same
   * value as This(). If there is a signature, and the signature didn't match
   * This() but one of its hidden prototypes, this will be the respective
   * hidden prototype.
   *
   * Note that this is not the prototype of This() on which the accessor
   * referencing this callback was found (which in V8 internally is often
   * referred to as holder [sic]).
   */
  V8_DEPRECATED(
      "V8 will stop providing access to hidden prototype (i.e. "
      "JSGlobalObject). Use This() instead. \n"
      "DO NOT try to workaround this by accessing JSGlobalObject via "
      "v8::Object::GetPrototype() - it'll be deprecated soon too. \n"
      "See http://crbug.com/333672197. ")
  V8_INLINE Local<Object> Holder() const;
  /** For construct calls, this returns the "new.target" value. */
  V8_INLINE Local<Value> NewTarget() const;
  /** Indicates whether this is a regular call or a construct call. */
  V8_INLINE bool IsConstructCall() const;
  /** The data argument specified when creating the callback. */
  V8_INLINE Local<Value> Data() const;
  /** The current Isolate. */
  V8_INLINE Isolate* GetIsolate() const;
  /** The ReturnValue for the call. */
  V8_INLINE ReturnValue<T> GetReturnValue() const;

  // This is a temporary replacement for Holder() added just for the purpose
  // of testing the deprecated Holder() machinery until it's removed for real.
  // DO NOT use it.
  V8_INLINE Local<Object> HolderSoonToBeDeprecated() const;

 private:
  friend class internal::FunctionCallbackArguments;
  friend class internal::CustomArguments<FunctionCallbackInfo>;
  friend class debug::ConsoleCallArguments;
  friend void internal::PrintFunctionCallbackInfo(void*);

  static constexpr int kHolderIndex = 0;
  static constexpr int kIsolateIndex = 1;
  static constexpr int kContextIndex = 2;
  static constexpr int kReturnValueIndex = 3;
  static constexpr int kTargetIndex = 4;
  static constexpr int kNewTargetIndex = 5;
  static constexpr int kArgsLength = 6;

  static constexpr int kArgsLengthWithReceiver = kArgsLength + 1;

  // Codegen constants:
  static constexpr int kSize = 3 * internal::kApiSystemPointerSize;
  static constexpr int kImplicitArgsOffset = 0;
  static constexpr int kValuesOffset =
      kImplicitArgsOffset + internal::kApiSystemPointerSize;
  static constexpr int kLengthOffset =
      kValuesOffset + internal::kApiSystemPointerSize;

  static constexpr int kThisValuesIndex = -1;
  static_assert(ReturnValue<Value>::kIsolateValueIndex ==
                kIsolateIndex - kReturnValueIndex);

  V8_INLINE FunctionCallbackInfo(internal::Address* implicit_args,
                                 internal::Address* values, int length);

  // TODO(https://crbug.com/326505377): flatten the v8::FunctionCallbackInfo
  // object to avoid indirect loads through values_ and implicit_args_ and
  // reduce the number of instructions in the CallApiCallback builtin.
  internal::Address* implicit_args_;
  internal::Address* values_;
  internal::Address length_;
};

/**
 * The information passed to a property callback about the context
 * of the property access.
 */
template <typename T>
class PropertyCallbackInfo {
 public:
  /**
   * \return The isolate of the property access.
   */
  V8_INLINE Isolate* GetIsolate() const;

  /**
   * \return The data set in the configuration, i.e., in
   * `NamedPropertyHandlerConfiguration` or
   * `IndexedPropertyHandlerConfiguration.`
   */
  V8_INLINE Local<Value> Data() const;

  /**
   * \return The receiver. In many cases, this is the object on which the
   * property access was intercepted. When using
   * `Reflect.get`, `Function.prototype.call`, or similar functions, it is the
   * object passed in as receiver or thisArg.
   *
   * \code
   *  void GetterCallback(Local<Name> name,
   *                      const v8::PropertyCallbackInfo<v8::Value>& info) {
   *     auto context = info.GetIsolate()->GetCurrentContext();
   *
   *     v8::Local<v8::Value> a_this =
   *         info.This()
   *             ->GetRealNamedProperty(context, v8_str("a"))
   *             .ToLocalChecked();
   *     v8::Local<v8::Value> a_holder =
   *         info.Holder()
   *             ->GetRealNamedProperty(context, v8_str("a"))
   *             .ToLocalChecked();
   *
   *    CHECK(v8_str("r")->Equals(context, a_this).FromJust());
   *    CHECK(v8_str("obj")->Equals(context, a_holder).FromJust());
   *
   *    info.GetReturnValue().Set(name);
   *  }
   *
   *  v8::Local<v8::FunctionTemplate> templ =
   *  v8::FunctionTemplate::New(isolate);
   *  templ->InstanceTemplate()->SetHandler(
   *      v8::NamedPropertyHandlerConfiguration(GetterCallback));
   *  LocalContext env;
   *  env->Global()
   *      ->Set(env.local(), v8_str("obj"), templ->GetFunction(env.local())
   *                                           .ToLocalChecked()
   *                                           ->NewInstance(env.local())
   *                                           .ToLocalChecked())
   *      .FromJust();
   *
   *  CompileRun("obj.a = 'obj'; var r = {a: 'r'}; Reflect.get(obj, 'x', r)");
   * \endcode
   */
  V8_INLINE Local<Object> This() const;

  /**
   * \return The object in the prototype chain of the receiver that has the
   * interceptor. Suppose you have `x` and its prototype is `y`, and `y`
   * has an interceptor. Then `info.This()` is `x` and `info.Holder()` is `y`.
   * The Holder() could be a hidden object (the global object, rather
   * than the global proxy).
   *
   * \note For security reasons, do not pass the object back into the runtime.
   */
  V8_DEPRECATE_SOON(
      "V8 will stop providing access to hidden prototype (i.e. "
      "JSGlobalObject). Use HolderV2() instead. \n"
      "DO NOT try to workaround this by accessing JSGlobalObject via "
      "v8::Object::GetPrototype() - it'll be deprecated soon too. \n"
      "See http://crbug.com/333672197. ")
  V8_INLINE Local<Object> Holder() const;

  /**
   * \return The object in the prototype chain of the receiver that has the
   * interceptor. Suppose you have `x` and its prototype is `y`, and `y`
   * has an interceptor. Then `info.This()` is `x` and `info.Holder()` is `y`.
   * In case the property is installed on the global object the Holder()
   * would return the global proxy.
   */
  V8_INLINE Local<Object> HolderV2() const;

  /**
   * \return The return value of the callback.
   * Can be changed by calling Set().
   * \code
   * info.GetReturnValue().Set(...)
   * \endcode
   *
   */
  V8_INLINE ReturnValue<T> GetReturnValue() const;

  /**
   * \return True if the intercepted function should throw if an error occurs.
   * Usually, `true` corresponds to `'use strict'`.
   *
   * \note Always `false` when intercepting `Reflect.set()`
   * independent of the language mode.
   */
  V8_INLINE bool ShouldThrowOnError() const;

 private:
  template <typename U>
  friend class PropertyCallbackInfo;
  friend class MacroAssembler;
  friend class internal::PropertyCallbackArguments;
  friend class internal::CustomArguments<PropertyCallbackInfo>;
  friend void internal::PrintPropertyCallbackInfo(void*);

  static constexpr int kPropertyKeyIndex = 0;
  static constexpr int kShouldThrowOnErrorIndex = 1;
  static constexpr int kHolderIndex = 2;
  static constexpr int kIsolateIndex = 3;
  static constexpr int kHolderV2Index = 4;
  static constexpr int kReturnValueIndex = 5;
  static constexpr int kDataIndex = 6;
  static constexpr int kThisIndex = 7;
  static constexpr int kArgsLength = 8;

  static constexpr int kSize = kArgsLength * internal::kApiSystemPointerSize;

  explicit PropertyCallbackInfo() = default;

  mutable internal::Address args_[kArgsLength];
};

using FunctionCallback = void (*)(const FunctionCallbackInfo<Value>& info);

// --- Implementation ---

template <typename T>
ReturnValue<T>::ReturnValue(internal::Address* slot) : value_(slot) {}

template <typename T>
void ReturnValue<T>::SetInternal(internal::Address value) {
#if V8_STATIC_ROOTS_BOOL
  using I = internal::Internals;
  // Ensure that the upper 32-bits are not modified. Compiler should be
  // able to optimize this to a store of a lower 32-bits of the value.
  // This is fine since the callback can return only JavaScript values which
  // are either Smis or heap objects allocated in the main cage.
  *value_ = I::DecompressTaggedField(*value_, I::CompressTagged(value));
#else
  *value_ = value;
#endif  // V8_STATIC_ROOTS_BOOL
}

template <typename T>
template <typename S>
void ReturnValue<T>::Set(const Global<S>& handle) {
  static_assert(std::is_base_of<T, S>::value, "type check");
  if (V8_UNLIKELY(handle.IsEmpty())) {
    SetDefaultValue();
  } else {
    SetInternal(handle.ptr());
  }
}

template <typename T>
template <typename S>
void ReturnValue<T>::SetNonEmpty(const Global<S>& handle) {
  static_assert(std::is_base_of<T, S>::value, "type check");
#ifdef V8_ENABLE_CHECKS
  internal::VerifyHandleIsNonEmpty(handle.IsEmpty());
#endif  // V8_ENABLE_CHECKS
  SetInternal(handle.ptr());
}

template <typename T>
template <typename S>
void ReturnValue<T>::Set(const BasicTracedReference<S>& handle) {
  static_assert(std::is_base_of<T, S>::value, "type check");
  if (V8_UNLIKELY(handle.IsEmpty())) {
    SetDefaultValue();
  } else {
    SetInternal(handle.ptr());
  }
}

template <typename T>
template <typename S>
void ReturnValue<T>::SetNonEmpty(const BasicTracedReference<S>& handle) {
  static_assert(std::is_base_of<T, S>::value, "type check");
#ifdef V8_ENABLE_CHECKS
  internal::VerifyHandleIsNonEmpty(handle.IsEmpty());
#endif  // V8_ENABLE_CHECKS
  SetInternal(handle.ptr());
}

template <typename T>
template <typename S>
void ReturnValue<T>::Set(const Local<S> handle) {
  // "V8_DEPRECATE_SOON" this method if |T| is |void|.
#ifdef V8_IMMINENT_DEPRECATION_WARNINGS
  static constexpr bool is_allowed_void = false;
  static_assert(!std::is_void<T>::value,
                "ReturnValue<void>::Set(const Local<S>) is deprecated. "
                "Do nothing to indicate that the operation succeeded or use "
                "SetFalse() to indicate that the operation failed (don't "
                "forget to handle info.ShouldThrowOnError()). "
                "See http://crbug.com/348660658 for details.");
#else
  static constexpr bool is_allowed_void = std::is_void<T>::value;
#endif  // V8_IMMINENT_DEPRECATION_WARNINGS
  static_assert(is_allowed_void || std::is_base_of<T, S>::value, "type check");
  if (V8_UNLIKELY(handle.IsEmpty())) {
    SetDefaultValue();
  } else if constexpr (is_allowed_void) {
    // Simulate old behaviour for "v8::AccessorSetterCallback" for which
    // it was possible to set the return value even for ReturnValue<void>.
    Set(handle->BooleanValue(GetIsolate()));
  } else {
    SetInternal(handle.ptr());
  }
}

template <typename T>
template <typename S>
void ReturnValue<T>::SetNonEmpty(const Local<S> handle) {
  // "V8_DEPRECATE_SOON" this method if |T| is |void|.
#ifdef V8_IMMINENT_DEPRECATION_WARNINGS
  static constexpr bool is_allowed_void = false;
  static_assert(!std::is_void<T>::value,
                "ReturnValue<void>::SetNonEmpty(const Local<S>) is deprecated. "
                "Do nothing to indicate that the operation succeeded or use "
                "SetFalse() to indicate that the operation failed (don't "
                "forget to handle info.ShouldThrowOnError()). "
                "See http://crbug.com/348660658 for details.");
#else
  static constexpr bool is_allowed_void = std::is_void<T>::value;
#endif  // V8_IMMINENT_DEPRECATION_WARNINGS
  static_assert(is_allowed_void || std::is_base_of<T, S>::value, "type check");
#ifdef V8_ENABLE_CHECKS
  internal::VerifyHandleIsNonEmpty(handle.IsEmpty());
#endif  // V8_ENABLE_CHECKS
  if constexpr (is_allowed_void) {
    // Simulate old behaviour for "v8::AccessorSetterCallback" for which
    // it was possible to set the return value even for ReturnValue<void>.
    Set(handle->BooleanValue(GetIsolate()));
  } else {
    SetInternal(handle.ptr());
  }
}

template <typename T>
void ReturnValue<T>::Set(double i) {
  static_assert(std::is_base_of<T, Number>::value, "type check");
  SetNonEmpty(Number::New(GetIsolate(), i));
}

template <typename T>
void ReturnValue<T>::Set(int16_t i) {
  static_assert(std::is_base_of<T, Integer>::value, "type check");
  using I = internal::Internals;
  static_assert(I::IsValidSmi(std::numeric_limits<int16_t>::min()));
  static_assert(I::IsValidSmi(std::numeric_limits<int16_t>::max()));
  SetInternal(I::IntegralToSmi(i));
}

template <typename T>
void ReturnValue<T>::Set(int32_t i) {
  static_assert(std::is_base_of<T, Integer>::value, "type check");
  if (const auto result = internal::Internals::TryIntegralToSmi(i)) {
    SetInternal(*result);
    return;
  }
  SetNonEmpty(Integer::New(GetIsolate(), i));
}

template <typename T>
void ReturnValue<T>::Set(int64_t i) {
  static_assert(std::is_base_of<T, Integer>::value, "type check");
  if (const auto result = internal::Internals::TryIntegralToSmi(i)) {
    SetInternal(*result);
    return;
  }
  SetNonEmpty(Number::New(GetIsolate(), static_cast<double>(i)));
}

template <typename T>
void ReturnValue<T>::Set(uint16_t i) {
  static_assert(std::is_base_of<T, Integer>::value, "type check");
  using I = internal::Internals;
  static_assert(I::IsValidSmi(std::numeric_limits<uint16_t>::min()));
  static_assert(I::IsValidSmi(std::numeric_limits<uint16_t>::max()));
  SetInternal(I::IntegralToSmi(i));
}

template <typename T>
void ReturnValue<T>::Set(uint32_t i) {
  static_assert(std::is_base_of<T, Integer>::value, "type check");
  if (const auto result = internal::Internals::TryIntegralToSmi(i)) {
    SetInternal(*result);
    return;
  }
  SetNonEmpty(Integer::NewFromUnsigned(GetIsolate(), i));
}

template <typename T>
void ReturnValue<T>::Set(uint64_t i) {
  static_assert(std::is_base_of<T, Integer>::value, "type check");
  if (const auto result = internal::Internals::TryIntegralToSmi(i)) {
    SetInternal(*result);
    return;
  }
  SetNonEmpty(Number::New(GetIsolate(), static_cast<double>(i)));
}

template <typename T>
void ReturnValue<T>::Set(bool value) {
  static_assert(std::is_void<T>::value || std::is_base_of<T, Boolean>::value,
                "type check");
  using I = internal::Internals;
#if V8_STATIC_ROOTS_BOOL
#ifdef V8_ENABLE_CHECKS
  internal::PerformCastCheck(
      internal::ValueHelper::SlotAsValue<Value, true>(value_));
#endif  // V8_ENABLE_CHECKS
  SetInternal(value ? I::StaticReadOnlyRoot::kTrueValue
                    : I::StaticReadOnlyRoot::kFalseValue);
#else
  int root_index;
  if (value) {
    root_index = I::kTrueValueRootIndex;
  } else {
    root_index = I::kFalseValueRootIndex;
  }
  *value_ = I::GetRoot(GetIsolate(), root_index);
#endif  // V8_STATIC_ROOTS_BOOL
}

template <typename T>
void ReturnValue<T>::SetDefaultValue() {
  using I = internal::Internals;
  if constexpr (std::is_same_v<void, T> || std::is_same_v<v8::Boolean, T>) {
    Set(true);
  } else if constexpr (std::is_same_v<v8::Integer, T>) {
    SetInternal(I::IntegralToSmi(0));
  } else {
    static_assert(std::is_same_v<v8::Value, T> || std::is_same_v<v8::Array, T>);
#if V8_STATIC_ROOTS_BOOL
    SetInternal(I::StaticReadOnlyRoot::kUndefinedValue);
#else
    *value_ = I::GetRoot(GetIsolate(), I::kUndefinedValueRootIndex);
#endif  // V8_STATIC_ROOTS_BOOL
  }
}

template <typename T>
void ReturnValue<T>::SetNull() {
  static_assert(std::is_base_of<T, Primitive>::value, "type check");
  using I = internal::Internals;
#if V8_STATIC_ROOTS_BOOL
#ifdef V8_ENABLE_CHECKS
  internal::PerformCastCheck(
      internal::ValueHelper::SlotAsValue<Value, true>(value_));
#endif  // V8_ENABLE_CHECKS
  SetInternal(I::StaticReadOnlyRoot::kNullValue);
#else
  *value_ = I::GetRoot(GetIsolate(), I::kNullValueRootIndex);
#endif  // V8_STATIC_ROOTS_BOOL
}

template <typename T>
void ReturnValue<T>::SetUndefined() {
  static_assert(std::is_base_of<T, Primitive>::value, "type check");
  using I = internal::Internals;
#if V8_STATIC_ROOTS_BOOL
#ifdef V8_ENABLE_CHECKS
  internal::PerformCastCheck(
      internal::ValueHelper::SlotAsValue<Value, true>(value_));
#endif  // V8_ENABLE_CHECKS
  SetInternal(I::StaticReadOnlyRoot::kUndefinedValue);
#else
  *value_ = I::GetRoot(GetIsolate(), I::kUndefinedValueRootIndex);
#endif  // V8_STATIC_ROOTS_BOOL
}

template <typename T>
void ReturnValue<T>::SetFalse() {
  static_assert(std::is_void<T>::value || std::is_base_of<T, Boolean>::value,
                "type check");
  using I = internal::Internals;
#if V8_STATIC_ROOTS_BOOL
#ifdef V8_ENABLE_CHECKS
  internal::PerformCastCheck(
      internal::ValueHelper::SlotAsValue<Value, true>(value_));
#endif  // V8_ENABLE_CHECKS
  SetInternal(I::StaticReadOnlyRoot::kFalseValue);
#else
  *value_ = I::GetRoot(GetIsolate(), I::kFalseValueRootIndex);
#endif  // V8_STATIC_ROOTS_BOOL
}

template <typename T>
void ReturnValue<T>::SetEmptyString() {
  static_assert(std::is_base_of<T, String>::value, "type check");
  using I = internal::Internals;
#if V8_STATIC_ROOTS_BOOL
#ifdef V8_ENABLE_CHECKS
  internal::PerformCastCheck(
      internal::ValueHelper::SlotAsValue<Value, true>(value_));
#endif  // V8_ENABLE_CHECKS
  SetInternal(I::StaticReadOnlyRoot::kEmptyString);
#else
  *value_ = I::GetRoot(GetIsolate(), I::kEmptyStringRootIndex);
#endif  // V8_STATIC_ROOTS_BOOL
}

template <typename T>
Isolate* ReturnValue<T>::GetIsolate() const {
  return *reinterpret_cast<Isolate**>(&value_[kIsolateValueIndex]);
}

template <typename T>
Local<Value> ReturnValue<T>::Get() const {
  return Local<Value>::New(GetIsolate(),
                           internal::ValueHelper::SlotAsValue<Value>(value_));
}

template <typename T>
template <typename S>
void ReturnValue<T>::Set(S* whatever) {
  static_assert(sizeof(S) < 0, "incompilable to prevent inadvertent misuse");
}

template <typename T>
FunctionCallbackInfo<T>::FunctionCallbackInfo(internal::Address* implicit_args,
                                              internal::Address* values,
                                              int length)
    : implicit_args_(implicit_args), values_(values), length_(length) {}

template <typename T>
Local<Value> FunctionCallbackInfo<T>::operator[](int i) const {
  // values_ points to the first argument (not the receiver).
  if (i < 0 || Length() <= i) return Undefined(GetIsolate());
  return Local<Value>::FromSlot(values_ + i);
}

template <typename T>
Local<Object> FunctionCallbackInfo<T>::This() const {
  // values_ points to the first argument (not the receiver).
  return Local<Object>::FromSlot(values_ + kThisValuesIndex);
}

template <typename T>
Local<Object> FunctionCallbackInfo<T>::HolderSoonToBeDeprecated() const {
  return Local<Object>::FromSlot(&implicit_args_[kHolderIndex]);
}

template <typename T>
Local<Object> FunctionCallbackInfo<T>::Holder() const {
  return HolderSoonToBeDeprecated();
}

template <typename T>
Local<Value> FunctionCallbackInfo<T>::NewTarget() const {
  return Local<Value>::FromSlot(&implicit_args_[kNewTargetIndex]);
}

template <typename T>
Local<Value> FunctionCallbackInfo<T>::Data() const {
  auto target = Local<v8::Data>::FromSlot(&implicit_args_[kTargetIndex]);
  return api_internal::GetFunctionTemplateData(GetIsolate(), target);
}

template <typename T>
Isolate* FunctionCallbackInfo<T>::GetIsolate() const {
  return *reinterpret_cast<Isolate**>(&implicit_args_[kIsolateIndex]);
}

template <typename T>
ReturnValue<T> FunctionCallbackInfo<T>::GetReturnValue() const {
  return ReturnValue<T>(&implicit_args_[kReturnValueIndex]);
}

template <typename T>
bool FunctionCallbackInfo<T>::IsConstructCall() const {
  return !NewTarget()->IsUndefined();
}

template <typename T>
int FunctionCallbackInfo<T>::Length() const {
  return static_cast<int>(length_);
}

template <typename T>
Isolate* PropertyCallbackInfo<T>::GetIsolate() const {
  return *reinterpret_cast<Isolate**>(&args_[kIsolateIndex]);
}

template <typename T>
Local<Value> PropertyCallbackInfo<T>::Data() const {
  return Local<Value>::FromSlot(&args_[kDataIndex]);
}

template <typename T>
Local<Object> PropertyCallbackInfo<T>::This() const {
  return Local<Object>::FromSlot(&args_[kThisIndex]);
}

template <typename T>
Local<Object> PropertyCallbackInfo<T>::Holder() const {
  return Local<Object>::FromSlot(&args_[kHolderIndex]);
}

namespace api_internal {
// Returns JSGlobalProxy if holder is JSGlobalObject or unmodified holder
// otherwise.
V8_EXPORT internal::Address ConvertToJSGlobalProxyIfNecessary(
    internal::Address holder);
}  // namespace api_internal

template <typename T>
Local<Object> PropertyCallbackInfo<T>::HolderV2() const {
  using I = internal::Internals;
  if (!I::HasHeapObjectTag(args_[kHolderV2Index])) {
    args_[kHolderV2Index] =
        api_internal::ConvertToJSGlobalProxyIfNecessary(args_[kHolderIndex]);
  }
  return Local<Object>::FromSlot(&args_[kHolderV2Index]);
}

template <typename T>
ReturnValue<T> PropertyCallbackInfo<T>::GetReturnValue() const {
  return ReturnValue<T>(&args_[kReturnValueIndex]);
}

template <typename T>
bool PropertyCallbackInfo<T>::ShouldThrowOnError() const {
  using I = internal::Internals;
  if (args_[kShouldThrowOnErrorIndex] !=
      I::IntegralToSmi(I::kInferShouldThrowMode)) {
    return args_[kShouldThrowOnErrorIndex] != I::IntegralToSmi(I::kDontThrow);
  }
  return v8::internal::ShouldThrowOnError(
      reinterpret_cast<v8::internal::Isolate*>(GetIsolate()));
}

}  // namespace v8

#endif  // INCLUDE_V8_FUNCTION_CALLBACK_H_